In the proposed grant period, we shall continue efforts to define the mechanism of thyroid hormone action at the cellular level. Emphasis will be placed on an elucidation of the nature and function of hepatic S14, a protein coded buy an mRNA which is rapidly responsive to thyroid hormone and carbohydrate administration. We shall attempt to define the nature the factors which regulate the expression of the gene for S14 and determine the basis of marked circadian variation of its mRNA. We plan to isolate the protein, define its subcellular localization, and deduce its function in a broken cell preparation. We shall attempt to determine to what extent T3 induces specific mRNA's by augmenting gene transcription or by stabilizing the mature or precursor mRNA. We shall extend ongoing studies demonstrating DNAse hypersensitive sites in those rat tissues which respond to T3 with an induction of mRNAS14. Efforts will be made to identify the specific nuclear proteins which may be responsible for the creation of the hypersensitive sites. In conjunction with these experiments, we propose renewed efforts to isolate the T3- nuclear receptor and determine the precise role of this protein in the initiation mechanism. Appropriate comparisons will be made between the hepatic mechanism under study in this laboratory and T3 induction of the mRNA for growth hormone in the pituitary. Such studies should help to reconcile apparent differences in the induction mechanism as inferred from recent reports (transcription vs. RNA stabilization; requirement for ongoing protein synthesis). We shall also try to develop a wider spectrum of model systems for the study of thyroid hormone action at the cellular level. We shall examine the effects of T3 on fat and the central nervous system using both two-dimensional mRNA activity profiles and hybridization techniques. Lastly, we are planning to continue ongoing clinical studies designed to define the plasma hormone signal responsible for pituitary suppression in man. Further , we shall apply the techniques of two-dimensional mRNA profiling to analyze the level and patterns of high abundancy sequences in human mononuclear cells derived from patients with thyroidal disease and patients with nonthyroidal catabolic disorders who exhibit lowered levels of circulating thyroid hormones. Such studies may reveal the physiological significance of the "low-T3 state".